Transport in the tokamak plasma edge

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:5829371

Vold, E L

Experimental observations characterize the edge plasma or boundary layer in magnetically confined plasmas as a region of great complexity. Evidence suggests the edge physics plays a key role in plasma confinement although the mechanism remains unresolved. This study focuses on issues in two areas: observed poloidal asymmetries in the Scrape Off Layer (SOL) edge plasma and the physical nature of the plasma-neutral recycling. A computational model solves the coupled two dimensional partial differential equations governing the plasma fluid density, parallel and radial velocities, electron and ion temperatures and neutral density under assumptions of toroidal symmetry, ambipolarity, anomalous diffusive radial flux, and neutral-ion thermal equilibrium. Drift flow and plasma potential are calculated as dependent quantities. Computational results are compared to experimental data for the CCT and TEXTOR:ALT-II tokamak limiter cases. Comparisons show drift flux is a major component of the poloidal flow in the SOL along the tangency/separatrix. Plasma-neutral recycling is characterized in several tokamak divertors, including the C-MOD device using magnetic flux surface coordinates. Recycling is characterized by time constant, {tau}{sub rc}, on the order of tens of milliseconds. Heat flux transients from the core into the edge on shorter time scales significantly increase the plasma temperatures at the target and may increase sputtering. Recycling conditions in divertors vary considerably depending on recycled flux to the core. The high density, low temperature solution requires that the neutral mean free path be small compared to the divertor target to x-point distance. The simulations and analysis support H-mode confinement and transition models based on the recycling divertor solution bifurcation.

• Research Organization: California Univ., Los Angeles, CA (USA)
• OSTI ID: 5829371
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700101* -- Fusion Energy-- Plasma Research-- Confinement
Heating
& Production
ASYMMETRY
BOUNDARY LAYERS
CLOSED PLASMA DEVICES
COMPARATIVE EVALUATIONS
CONFINEMENT
DIVERTORS
EDGE LOCALIZED MODES
ELECTRON TEMPERATURE
GEOMETRY
H-MODE PLASMA CONFINEMENT
HEAT FLUX
INSTABILITY
ION TEMPERATURE
LAYERS
LIMITERS
MAGNETIC CONFINEMENT
MATHEMATICS
PLASMA CONFINEMENT
PLASMA DENSITY
PLASMA DRIFT
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PLASMA SCRAPE-OFF LAYER
PLASMA SIMULATION
POLOIDAL FIELD DIVERTORS
SIMULATION
SPUTTERING
TEXTOR TOKAMAK
THERMONUCLEAR DEVICES
TOKAMAK DEVICES